Method for impact-forming slipper-type pistons



June 18, 1963 c. A. SPARKS 3,093,890

METHOD FOR IMPACT-FORMING SLIPPER-TYPE PISTONS Filed March 4, 1958 2 Sheets-Sheet 1 I II 2; INVENTOR.

6250M;- Hen/02 5242/45 A. BY W W June 18, 1963 c. A. SPARKS 3,093,390

METHOD FOR IMPACT-FORMING sLIPPER-TYPE PISTONS Filed March 4, 1958 2 Sheets-Sheet 2 fir a,

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' CLEO/V5 Aer/we Jwrezs M KW7 United States Patent ()fiiee 3,093,890 Patented June 18, 1963 3,093,890 METHOD FOR IMPACT-FORMING SLIPPER-TYPE PISTONS Cleone Arthur Sparks, 1979 E. Colorado Blvd., Pasadena, Calif. Filed Mar. 4, 1958, Ser. No. 719,006 2 Claims. (l. 29-156.5)

This invention relates to a method of and apparatus for making a forged slipper-type piston having integral head, skirt and wrist pin bosses by a single impact extrusion operation.

Although many attempts had been made to manufacture forged pistons for internal combustion engines, the prior attempts required a series of steps and progressive dies (as in Patent No. 2,344,358) and did not utilize grain structure of the metal to good advantage until the advent of Patent No. 2,740,519 which taught the successful manufacture of pistons having integral head, skirt and wrist pin bosses by a single impact extrusion operation. Great numbers of pistons have been manufactured by the method and apparatus of Patent No. 2,740,519, but the pistons so made were of the normal type wherein the skirt is of uniform length. More recently, the development of more compact engines has required the rapid and economical manufacture of pistons of the slipper type wherein the skirt is provided with a long, load-bearing portion adapted to distribute power stroke pressures upon the side wall of a cylinder, and with short skirt portions adjacent the wrist pin bosses, these short portions being contoured (in most instances) to provide necessary clearance for countenweights carried by the crank shaft.

The present invention embodies the principles of my prior patent and in addition permits the direct production of slipper-type pistons without waste of metal and without the necessity of individually machining each piston blank to form the cut-away or short skirt portion. The prior disclosure (Patent No. 2,740,519) did not teach the application of a compressive forming pressure to the end face of the skirt; this invention utilizes the step of applying includes preheating of the metal slugs of predetermined weight, lubrication of the punch and impact forming during which flow of metal into skirt portions is promoted while flow of metal into areas adjacent wrist pin bosses is restricted and retarded by application of forces which form contoured end faces of short skirt portions adjacent the integral bosses. Flow of metal into wrist pin boss recesses is promoted by venting such recesses. As a result of such concurrent and virtually simultaneous steps, a dense, strong, lightweight piston blank is obtained which needs little machining.

An object of the present invention is the provision of a novel method of an apparatus for producing a forged, slipper-type piston.

Another object is to provide a method of and apparatus for making differently contoured, forged, slipper-type pistons which may be of various sizes.

A further object is the provision of a method of and apparatus for making a unitary, forged, slipper-type piston with an integral head, skirt and wrist pin bosses, the skirt including skirt portions of short, predetermined length in the regions of the bosses and a longer skirt in regions between the bosses.

Another object is the provision of a method of and apparatus for making a forged slipper-type piston whereby the formed piston blank is easily stripped from the male pressure to desired areas of the end face of the skirt to 7,

produced deformation, splitting or weakening of the skirt.

This is not true in the instant case because the metal of the skirt portions adjacent the bosses has been subjected to impact and forming, and perfect contact exists between the slipper-forming elements and such skirt portions, permitting ready withdrawal of the male punch from the formed piston without the generation of any strains in the blank.

The apparatus, in general, comprises a suitable die and a male punch for cooperation therewith. The die is preferably provided with a removable liner, so that a single die block may be used in making variously sized piston blanks. The male punch is preferably provided with vents which insure complete filling of wrist pin boss recesses with metal; In addition, the apparatus includes a combined forming and stripping ring which, in combination with the die and punch, forms the short skirt portions, insures that the punch is accurately bottomed (thereby establishing desired head thickness) and strips the formed blank from the punch. i

The method of operation hereinafter disclosed in detail punch without damaging the skirt portions of the piston.

Another object is the provision of an apparatus for making a forged, slipper-type piston and having a single means for restraining flow of metal into skirt portions while enhancing flow of metal into wrist pin boss recesses, contouring end faces of short skirt portions and for stripping the piston black from the male punch when it is withdrawn from the cavity of the die.

Another object is to provide an apparatus for making a forged, slipper-type piston in which the male forging punch has wrist pin boss recesses which are vented to promote the flow of metal thereinto during the forging operation.

A final and more specific object of the present invention is the provision ofa method of and apparatus for making a unitary, forged, slipper-type piston with an integral head, skirt and wrist pin bosses, the skirt including skirt portions of short, predetermined length in the regions of the bosses and a longer skirt in the regions between the bosses, by a single impact extruction operation of a male punch having Wrist pin boss recesses upon a slug of metal in a die.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a side elevation of an exemplary slipper-type piston.

FIG. 2 illustrates an exemplary apparatus by which the method may be carried out, a portion of the figure being in side elevation and a portion in vertical section, the punch being shown raised before delivery of its impact upon a slug of metal to be formed.

FIG. 3 is a plan view taken from plane III-III of FIG. 2.

piston which .can be made in accordance with this invention. In each instance the piston v1 has .a head .2 (which has a contour designed to fit the valving, combustion chamber dome, etc. of the engine in which it is to be used) and an integral skirt including integral, opposing wrist pin bosses including the wrist pin boss 4 in FIG. 1 the skirt portions 5 adjacent the wrist pin bosses being short and terminating in contoured end faces 6 while skirt portions 7 between said bosses are longer .and thicker. The entire inner surface 9 is a forged unmachined surface; very little machining need be done on the external surface and head of the forged piston blank other than the cutting of the ring grooves 11, the boring of Wrist pin bores 12 and a finishing of the end faces 8' of the long skirt portions 7. End faces 6 of the short skirt portions are formed during forging, and very little ifany, finishing is required there. The proportions of the piston and contour of end faces 6 will vary. It may be noted that the wall of the piston in the pad area (where ring grooves 11 are cut) is inherently thicker. The forged piston blank is of a predetermined height or distance from contoured end face 6 to the outer surface of the head 2. The impact forging method of this invention produces lands (between ring grooves) in which the flow lines are such as to reduce loading on the lands.

An exemplary apparatus by means of which the method of the present invention can be carried out is illustrated in the drawings. The essential elements comprise a die block 20 and male punch 30 and a slipper-forming and blank stripping ring 40 movably mounted between the die block and the punch when the punch is in raised position as illustrated in FIG. 2. It is to be understood that the die block 20 is mounted on a firm foundation and the male punch 30 is actuated by a suitable press. In the manufacture of slipper-type pistons from class A forging stock, aluminum alloys, etc., it is desirable to employ a press capable of exerting forging pressures of from about 450 to 900 tons, depending upon size blank which is being forged.

The die block 20 is provided with a cavity 21; the walls of the cavity are formed by a removable die liner 22 press fitted into the die block. Die block and its liner are then firmly mounted upon a die pad 23. A knock-out base 24 having an upper surface 25 contoured in accordance with the shape which is to be imparted to the outer surface of the piston head 'is removably positioned within the cavity 21, the upper surface of the knock-out block 24 and the inner walls of the die liner 22 thereby forming the walls of the die cavity 21. A vertical reciprocable knock-out bar 26 operates through a suitable bore in the die pad 23 for the purpose of moving the knock-out base 24 upwardly in the cavity at the end of a forming operation. It will be noted that the present arrangement permits various die liners and knock-out bases to be used in p the same die block, thereby permitting a great variety of pistons, difiering in shapes and sizes, to be made in the same die block.

As more clearly illustrated in FIG. 4, the knock-out base 24 may be provided with a small vent channel 27 for the purpose of eliminating air or preventing any air from being trapped. Such channel 27 may communicate with the bore in which the knock-out bar 26 operates.

The vertically reciprocatable male punch 30 has an external surface which forms the inner surface 9 of the slipper-type piston blank (the finished form of piston being illustrated in FIG. 1). The male punch 30 is therefore provided with a pair of opposing recesses 34 and 34' adapted to form the wrist pin bosses integrally with the skirt and the head. The punch 30 is provided with an outwardly extending .stop shoulder 31 and as previously indicated the entire punch is associated with a suitable press for downward movement into the die cavity 2'1 so as to perform impact extrusion upon a slug of metal placed within the die cavity.

In order to prevent the entrapment of air in the recesses 34 and 34' which form the integral wrist pin bosses of the piston blank, it .has .been found highly desirable to provide punch 30 with small bleeder channels or vent passageways such as 33 and 33' (shown to best advantage in FIG. 4), these passageways communicating the innermost portions of the recesses 34 and 34' with the atmosphere. In many instances, the end face of the punch 30 is provided with a number of recesses such as 35 and 36 (as illustrated in FIG. 4), these recesses being adapted to form ribs capable of suitably chilling or disseminating heat from the piston head. Again, in order to make certain that metal is properly forced into these recesses, additional channels such as 38 may communicate the recesses 35 and 36 either with the atmosphere or with the cross-channel 39 leading to the wrist pin boss recesses 34 and 34'.

Upstanding guide blocks 28, 28' and the like carried by the die block 20 guide the horizontally disposed slip per-forming and stripper ring 40 in its vertical motion. Each of the stationary vertically extending guide blocks 28, 28 and the like, may extend into a grove formed in the outer periphery of the stripping ring 40, such groove being preferably between a pair of cars such as 41 and 42, 41 and 42, etc. In order to maintain the ring 40 in an elevated position above the upper surface of a die block, the ring 40 may be suitably urged upwardly by means of springs. Certain of the cars such as the cars 42 may, for example, carry a downwardly extending open-ended housing tube 44 containing a spring 45. These housing tubes 44 may extend into suitable bores formed in the die block 20, the springs 45 thereby urging the entire ring upwardly. In order to limit upward movement of the slipper-forming and stripper ring 40, the other set of ears such as the cars 41, 41 and the like, may be provided with vertical bores through which extend vertical pins 46, the lower end of each pin being threadedly mounted in die block 20 while the upper end is provided with a stop head or nut 46.

The ring 40 is provided with a central aperture or opening 47 adapted to slida-bly receive the punch 30 and to fit said punch rather closely when the punch is in its fully bottomed position as illustrated in FIG. 4. The ring 40 is also of sufficient width so that in its lowermost position, shown in FIG. 4, it contacts the upper edge of the liner 22 and the upper surface of the die block 20. In such lowermost position, it will be noted that the shoulder 31 of the punch rests upon the ring 40. The ring therefore regulates and insures that the punch extend into the die cavity a suitable distance.

Downwardly extending from the slipper-forming ring 40 are the forming and stripping elements 48 and 48'. These stripping elements 48 and 48' are diametrically opposed and are positioned to be in transverse alignment with the wrist pin forming recesses 34 and 34 of the punch. When the punch is bottomed in its die as indicated in FIG. 4, these forming elements 48 and 48' of the ring 40 are directly above the wrist pin boss recesses and the lower surfaces of the elements 48 and 48', indicated at 49 and 49, respectively, impart the desired contour to the short skirt portions 5 of the piston blank and form the end faces 6 of such short skirt portions.

Any metal or alloy may be used in the manufacture of piston blanks; aluminum alloys of the 20-18 and 20-32 Class A forging stock type, magnesium alloys, magnesium thorium alloys, etc., have been used. Preferably, these various metals or alloys are first rolled into elongated bars so as to have the grain run longitudinally of the bars and then the bars are cut into disc-like shapes of predetermined weight and thickness. The diameter of these discs is substantially equal to the smallest diameter of the die cavity and when such disc or slug of metal is placed into the die cavity (in a position indicated by dash lines in FIG. 2), the grain now runs axially with respect to the die cavity. Preferably, these slugs are preheated to a temperature from between about 700 F. to 800 F.

During constant operation, the punch develops a temperature of about 600 F. at its head and a temperature of between about 400 F. and 450 F. immediately above the wrist pin boss recesses. Suitable temperatures are maintained in both the punch and the die by suitable heating and cooling conduits formed in the die block and in the punch. Reference can be made to my prior patent for an illustration of the manner in which both the die and the punch may be heated or cooled as the case may be.

In order to insure homogeneity in the piston blank, in order to make certain that the Wrist pin boss recesses, inwardly extending radiation fins and the like, are completely filled and formed, and in order to make certain that the skirt portions are properly made without weaknesses, cracks, deformations or wasted metal, the flow of metal in various parts of the space between the walls of the die cavity and the punch must be carefully controlled. It is necessary, for example, to restrain and impede the flow of metal into skirt portions immediately adjacent the bosses being formed and to facilitate flow of metal into the recesses of the male punch which form such bosses and into the portions of the space in which the thicker, longer skirt portions are to be formed. In large part, the flow of metal is promoted and retarded in the manner indicated by the use of the principles enunciated in my prior Patent No. 2,740,519. For example, in a transverse plane taken through the punch and die in a zone immediately above the wrist pin bosses (as illustrated in FIG. 4 and FIG. 6), the distance separating the inner wall of the cavity from the punch in Zones or areas between wrist pin bosses is appreciably greater than the distance separating the inner wall of the die cavity and the outer surface of the punch in areas immediately adjacent the wrist pin boss recess. The restriction or reduced width of the space between the punch and the inner walls of the cavity immediately adjacent the wrist pin boss recesses, restricts the flow of metal out of the recesses into the space adjacent thereto while the increased width of such space in zones between the recesses facilitates the flow of metal thereinto. Moreover, in accordance with the present invention, the downward impact of the punch is transmitted to the forming ring 40 and elements 48 and 48 which further impede and restrict the flow of metal immediately adjacent the recesses and actually compact the metal in the thin skirt portions adjacent such recesses. The elements 48 and 48 therefore not only contour the lower faces of the short skirt portions of the slipper-type piston but also insure that adequate metal flows into the wrist pin bosses and that the metal is not impeded from flowing into the longer skirt portions.

Prior to forming of piston blanks in accordance with the method and apparatus hereinabove described, it is desirable to spray or paint the male punch 30 with a suitable high temperature lubricant. Moreover, it is desirable that both the punch and the die be brought up to near actual working temperatures. Each slug of material fed into the die cavity should be properly preheated and should be of approximately the correct weight to completely fill the cavity when the punch is bottomed (as illustrated in FIG. 4). At the end of an impact extrusion, the punch is raised and the ring 40 follows the punch being urged upwardly by the biasing springs 45. In most instances, the formed blank tends to adhere to the punch and is raised with the punch. When the ring 40 has reached its upper limit (established by the stop guide rods 46 and nuts 46), it will be noted that the blank will be stripped ofi the punch, the bottom surfaces of forming elements 48 and 48 remaining in contact with and exerting pressure upon the end faces of the short skirt portions. The blank is therefore automatically removed and stripped from the male punch and since the stripping pressure is applied upon a compacted formed face or end face of the piston blank, no deformation, cracking or other weakening of the blank is obtained. It may be noted that this time the stationary guides 23 and 28, and the like, only extend about around the cavity permitting the blank to be readily removed from one side of the assembly. In some instances, however, the piston blank remains within the die cavity and the knock-out bar 26 can then be used to move the knock-out base 24 upwardlythereby raising the finished blank to a discharge and remove position.

Attention isagain drawn to the fact that in its bottomed position the shoulder-31 of the male punch 30 impacts the slipper-forming ring 40 which. in turn is impacted against the upper face of the die block and liner 22. A definite predetermined positioning of the punch within the die cavity is thus obtained. The thickness of the resulting piston head is established within very close tolerances. Very little machining need be done. The distance between the formed end face of the short skirt portions of the piston and the top of the head of the piston is also established with a great deal of accuracy.

It is to be understood that during impact forging under the conditions herein described, high pressures and great friction stresses are generated. It has been found desirable, in order to increase the service life of the punch, to make the punch with inserts of carbide base material or other suitable wear-resisting air hardening metallic composition at its high pressure areas, such as those where the punch forms the ring pad and adjacent the wrist pin bosses, where flow of metal is restricted. Air hardening metallic compositions which harden by cooling without quenching are known. Moreover the entire punch may be chrome plated to good advantage, dull plating being preferred to bright plating.

I claim:

1. The method of making a forged slipper type piston blank provided with a head, a skirt of predetermined non-uniform length and integral wrist pin bosses by a single impact extrusion operation of a male punch against a slug of metal in a die, comprising: applying impact forces to a slug of metal in a single impact extrusion operation by impacting a male punch against a slug of metal in a die to form a piston blank having a head, a skirt and integral wrist pin bosses and concurrently promoting flow of metal into areas of said blank between said wrist pin bosses to form thick skirt portions, restricting flow of metal into areas of said blank immediately adjacent said wrist pin bosses to form thin skirt port-ions adjacent each said wrist pin boss and preventing flow of metal into end face portions of said blank in the skirt adjacent the wrist pin bosses to form said skint of predetermined non-uniform length and to form end face portions of said skirt of predetermined length and configuration adjacent said bosses.

2. A method of making a unitary, forged, slipper type piston with intergal head, skirt and wrist pin bosses, said skirt including portions of short, predetermined length and contour in the region of the bosses and longer skirt portions in regions between bosses, comprising: placing a heated slug of metal in a female die having a non-cylindrical inner surface and applying a male punch against said slug of metal in a single impact extrustion operation, said punch having wrist pin boss recesses to form wrist pin bosses in the blank formed by said extrusion and concurrently promoting flow of metal into skirt portions in areas of the blank between wrist pin bosses, restricting flow of metal into skirt portions in areas of the blank immediately adjacent the wrist pin bosses and preventing how of metal to the end surface of the skirt being formed in said blank between the punch and die in areas thereof adjacent each of said bosses to provide a predetermined length and contour to such skirt in said areas.

References Cited in the file of this patent UNITED STATES PATENTS 1,490,849 Philip Apr. 15, 1924 (Other references on following page) UNITED STATES PATENTS Michel Apr. 1 9, 11932 Handler Nov. 28, 1933 Handler Dec. 17, 1935 Dempsey July 26, 1938 lcnz June 10, 1941 Sparks Nov. 4, 1941 Rice Oct. 19, 1948 Watson Jan. 26, 1954 Hammond July 20, 1954 Sparks Apr. 3, 1956 3 FOREIGN PATENTS Switzerland Mar. 31, 11935 OTHER REFERENCES Herb: Forging Aluminum Aircraft Pistons, Machinery, November 1945, pp. 149-152.

Material and Methods, August 1955, pp, 111-126, Impact (Cold) Extruded Parts. 

1. THE METHOD OF MAKING A FORGED SLIPPER-TYPE PISTON BLANK PROVIDED WITH A HEAD, A SKIRT OF PREDETERMINED NON-UNIFORM LENGTH AND INTEGRAL WRIST PIN BOSSES BY A SINGLE IMPACT EXTRUSION OPERATION OF A MALE PUNCH AGAINST A SLUG OF METAL IN A DIE, COMPRISING: APPLYING IMPACT FORCES TO A SLUG OF METAL IN A SINGLE IMPACT EXTRUSION OPERATION BY IMPACTING A MALE PUNCH AGAINST A SLUG OF METAL IN A DIE TO FORM A PISTON BLANK HAVING A HEAD, A SKIRT AND INTEGRAL WRIST PIN BOSSES AND CONCURRENTLY PROMOTING FLOW OF METAL INTO AREAS OF SAID BLANK BETWEEN SAID WRIST PIN BOSSES TO FORM THICK SKIRT PORTIONS, RESTRICTING FLOW OF METAL INTO AREAS OF SAID BLANK IMMEDIATELY ADJACENT SAID WRIST PIN BOSSES TO FORM THIN SKIRT PORTIONS ADJACENT EACH SAID WRIST PIN BOSS AND PREVENTING FLOW OF METAL INTO END FACE PORTIONS OF SAID BLANK IN THE SKIRT ADJACENT THE WRIST PIN BOSSES TO FORM SAID SKIRT OF PREDETERMINED NON-UNIFORM LENGTH AND TO FORM END FACE PORTIONS OF SAID SKIRT OF PREDETERMINED LENGTH AND CONFIGURATION ADJACENT SAID BOSSES. 